Robot arms that transport semiconductor wafers are known. Specifically, the robot arm inserts the semiconductor wafer into a process chamber, and removes the semiconductor wafer from the process chamber. A transfer chamber is connected to the process chamber. The robot arm is disposed in the transfer chamber. Semiconductor wafers are transferred between the transfer chamber and the process chamber by the robot arm. The transfer chamber corresponds to a small-sized clean room. The transfer chamber prevents impurities such as dust from adhering to the semiconductor wafers. The air (or gas) in the transfer chamber is kept clean. Furthermore, the transfer chamber interior may, in some cases, be maintained under a vacuum. The robot arm that operates within the transfer chamber is required to be a device that does not generate impurities.
The robot arm that transports the semiconductor wafers usually has two or more degrees of freedom. Typically, the robot arm is comprised of two links and a hand. In the present description, the two links will be called an upper arm link and a lower arm link. Typically, one end of the upper arm link is connected to an output shaft of a motor, and the other end of the upper arm link is connected to one end of the lower arm link. Furthermore, the other end of the lower arm link is connected to the hand. The upper arm link and the lower arm link are connected via a joint. The lower arm link and the hand are also connected via a joint. A bearing is mounted on each of the joints so that the links rotate smoothly. Examples of such robot arms are disclosed in Japanese Patent Application Publication No. 2000-150617 and Japanese Patent Application Publication No. 2000-195923. In robot arms that transport semiconductor wafers, the bearings mounted on the joints are shielded so that the transfer chamber interior is not contaminated.